When you want to use ORDER BY on an expression, you can
use either the display label assigned to the expression or an integer,
as Query and Query show. Figure 1: Query
SELECT customer_num, call_code, call_dtime,
res_dtime - call_dtime span
FROM cust_calls
ORDER BY span;
The query retrieves the same data from the cust_calls table
as ids_sqt_079.html#ids_sqt_079__sii-02-24543.
In the query, the ORDER BY clause causes the data to be displayed
in ascending order of the derived values in the span column,
as the result shows. Figure 2: Query result
customer_num call_code call_dtime span
127 I 1998-07-31 14:30
121 O 1998-07-10 14:05 0 00:01
106 D 1998-06-12 08:20 0 00:05
110 L 1998-07-07 10:24 0 00:06
116 I 1997-11-28 13:34 0 03:13
119 B 1998-07-01 15:00 0 17:21
116 I 1997-12-21 11:24 5 20:55
The following query uses an integer to represent
the result of the operation res_dtime - call_dtime and
retrieves the same rows that appear in the above result. Figure 3: Query
SELECT customer_num, call_code, call_dtime,
res_dtime - call_dtime span
FROM cust_calls
ORDER BY 4;